I. Field
The following description relates generally to wireless communications, and more particularly to employing constrained hopping of downlink (DL) reference signals in a Long Term Evolution (LTE) based wireless communication system.
II. Background
Wireless communication systems are widely deployed to provide various types of communication; for instance, voice and/or data can be provided via such wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources (e.g., bandwidth, transmit power, . . . ). For instance, a system can use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Orthogonal Frequency Division Multiplexing (OFDM), and others.
Generally, wireless multiple-access communication systems can simultaneously support communication for multiple access terminals. Each access terminal can communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to access terminals, and the reverse link (or uplink) refers to the communication link from access terminals to base stations. This communication link can be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
MIMO systems commonly employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas can be decomposed into NS independent channels, which can be referred to as spatial channels, where NS≦{NT,NR}. Each of the NS independent channels corresponds to a dimension. Moreover, MIMO systems can provide improved performance (e.g., increased spectral efficiency, higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and received antennas are utilized.
MIMO systems can support various duplexing techniques to divide forward and reverse link communications over a common physical medium. For instance, frequency division duplex (FDD) systems can utilize disparate frequency regions for forward and reverse link communications. Further, in time division duplex (TDD) systems, forward and reverse link communications can employ a common frequency region so that the reciprocity principle allows estimation of the forward link channel from reverse link channel.
Wireless communication systems oftentimes employ one or more base stations that provide a coverage area. A typical base station can transmit multiple data streams for broadcast, multicast and/or unicast services, wherein a data stream may be a stream of data that can be of independent reception interest to an access terminal. An access terminal within the coverage area of such base station can be employed to receive one, more than one, or all the data streams carried by the composite stream. Likewise, an access terminal can transmit data to the base station or another access terminal.
Oftentimes, frequency hopping and channel estimation are utilized with conventional wireless communication systems. Frequency hopping techniques can be used to alter frequencies upon which signal(s) are sent from base stations as a function of time. For example, if two base stations transmit respective signals upon a common frequency at a first time, two differing frequencies as yielded from frequency hopping can respectively be used by the two base stations for sending respective signals at a second time. Hence, frequency hopping can be employed to mitigate interference/frequency overlap between transmissions from disparate base stations, since without frequency hopping a plurality of base stations can transfer signal(s) using a common frequency at all or substantially all times. However, use of frequency hopping can detrimentally impact performance of channel estimation at access terminal(s). More particularly, unconstrained frequency hopping can inhibit access terminal(s) from averaging received signal(s) (e.g., from base station(s)) at a particular frequency location over time, where such averaging can enable access terminal(s) to reduce noise and interference levels from the received signal(s). Accordingly, conventional use of frequency hopping can detrimentally impact channel estimation by hampering an ability to reduce noise and interference, whereas lack of use of frequency hopping can negatively influence channel estimation since interference/frequency overlap between transmissions from at least a subset of differing base stations can result for all or most times.